Nanocrystallisation on the Surface of Superalloy in718 Component With a Commercial Shot Peening Process

Author:  Yijun Liu, Ben Mcgrory, Colin Mcgrory
Source:  ICSP-13
Doc ID:  2017047
Year of Publication:  2017
Abstract:  
Introduction: Since the early of 2000s, there has been significant interest in surface nanocrystallisation using the so-called surface mechanical attrition treatment (SMAT) [1]. Ultrasonic shot peening is one of the most common processes that functions at a frequency ranging from 50Hz to 20kHz, and has been proved effective to create nanograin structures on a variety of metallic materials: stainless steel, Ti-6Al-4V, aluminium alloys and Ni-based superalloys etc.[2,3]. However, ultrasonic peening has process limitations where complex features exist. Recently the conventional shot peening process has also been found capable to produce nanostructures on a metal surface [4,5,6], however, most studies were carried out in a laboratory scale, and there is a lack of systematic study on how to adopt this surface nanocrystallisation process to a large scale production using a commercial shot peening process. In industry, the process of shot peening is usually set up and established to treat a component surface by imparting large compressive stress into the surface of parts therefore improving fatigue life. By development of shot peening parameters, specifically shot size, shot energy and coverage, a successful adoption of the current commercial process can achieve a Nanocrystalline surface producing a step change and further enhancing part performance. Inconel 718 is a workhorse Ni-based superalloy often made into structural components subjected to various service conditions such as dynamic loading, fretting fatigue, wear and corrosive environments, all of which are sensitive to the microstructure and properties of the component surface. A nanocrystallized surface with grain size of 12 nm up to a depth of about 90 microns was created with an ultrasonic peening process in a peak aged Inconel718 superalloy [3]. However, there is a lack of information regarding a commercial shot peening process to produce a nanocrystallized surface in Inconel 718.